1C Rate Research Articles

Conducting LixPOy Interface Generated From Insulating Residual Lithium Compounds on LiNi0.8Mn0.1Co0.1O2 Surface Improves Cycle Life and Assists in Fast Cycling.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is the most promising cathode material for future Li-ion batteries (LIBs). However, the bulk and surface structural instabilities retard its commercial success. Surface chemical instability toward exposure to moisture (H2O and CO2) leads to the formation of residual lithium compounds (RLCs: Li2CO3, LiOH) on the surface. The alkaline RLCs form a resistive layer on the surface of NMC811 by undergoing parasitic side reactions with electrolytes. Herein, an "Adverse-to-Beneficial" approach is proposed to eliminate RLCs by chemically transforming them into a LixPOy (Li3PO4 and LiPO3) interface. The interface protects the NMC811 surface from moisture attack and unwanted side reactions with electrolytes. It enhances the cycle life by retaining 70% of the initial capacity after 300 cycles at a 0.5C rate and 60% after 500 cycles, even at a 5C rate in a voltage window of 3.0-4.3V versus Li+/Li. The coexistence of two Li-conducting phases lowers the voltage polarization of the kinetically sluggish H1 → M phase transition to unlock fast cycling, reduces cationic disorder, improves coulombic efficiency, enhances ion diffusion kinetics, and minimizes particle crack formation after long-term cycling. Hence, the LixPOy interface yields multifaceted benefits in the storage, processing, and electrochemistry of NMC811.

Boosting the rate performance of all-solid-state batteries with a novel double layer solid electrolyte

When compared to traditional liquid electrolytes, solid electrolytes face significant challenges due to insufficient ionic conductivity and poor interfacial contact. To overcome these challenges, a cathode-supported double layer gradient structured solid polymer electrolyte membrane is developed. This innovative design enhances the wetting ability of the solid electrolyte on the cathode, leading to improved rate performance. Furthermore, the double layer solid electrolyte enhances mechanical strength, ensuring excellent cycling performance. As a result, the LiFePO4/Li solid state battery demonstrates superior battery performances, for instance, it can achieve a discharge capacity of 121 mAh g−1 at a current rate of 5C, with a capacity retention of 99 % after 380 cycles. This work offers a promising strategy for further enhancing the performance of all solid-state batteries.

Enhancing electric field intensity of interfacial electric double layer to improve properties of solid electrolyte interface for sodium-ion batteries

The electrical double layer (EDL) provides a critical area, where the specific adsorption on the electrode dominates the initial structure and chemical composition of the solid electrolyte interface (SEI) film. Therefore, the SEI can be optimized by adjusting the properties of the EDL. Here, we regulate the properties of EDL to optimize the composition and morphology of the SEI film on the hard carbon anode surface by adding NaF with small molecule structure. The preferential accumulation of NaF additives on the electrode surface enhances the electric field intensity and promotes electrolyte decomposition. That is, the formed SEI film rich in inorganic NaF and B-O components, can significantly improve the storage capacity of sodium ions in the hard carbon anode and accelerate the rapid transport of sodium ions. This strategy enables the cycling capacity to improve by 13.5 %, and maintain a stable capacity retention rate of 86.2 % at the rate of 1C after 500 cycles, thereby extending the lifespan and increasing the capacity of the rechargeable battery. The strategy that utilizing small molecule additives to enhance the electric field intensity of EDL provides a new approach to improve the performances of SEI film and battery performances.

Comparative analysis of data-driven electric vehicle battery health models across different operating conditions

The work covers the development of a data-driven algorithm and computes the performance of learning models for lithium-ion battery state of health (SOH) estimation. A wide range of environmental and temperature conditions (15 °C, 25 °C, and 35 °C) at different charging and discharging rates of 1C and 2C are used for electric vehicle battery health estimation. The result of the tested data of cell ‘a’ is validated with a different set of cell ‘b’ on identical test parameters, and the results are tabulated and compared. At 25 °C, the mean absolute errors for the regression algorithms decision tree (DT), k-nearest neighbor (KNN), and random forest (RF) are 3.78641E-03, 3.62524E-03, and 6.16931E-03. The mean absolute percent error for regression algorithms DT, KNN, and RF is 1.48921E-03, 1.40631E-03, and 2.40260E-03. The root mean square error for regression algorithms DT, KNN, and RF is 1.26813E-02, 9.73320E-03, and 1.17238E-02, and the mean squared error for regression algorithms DT, KNN, and RF is 1.60816E-04, 9.47351E-05, and 1.37448E-04. The results show that the KNN and DT methods accurately estimate the SOH under diversified operating conditions in comparison with RF methods and can foster advanced battery health monitoring systems.

Experimental study of a novel guided sequential immersion cooling system for battery thermal management

Immersion cooling exhibits superior cooling performance compared to traditional battery thermal management systems (BTMS). However, a significant challenge of immersion cooling is the spatial variation of temperature within both the coolant and lithium-ion batteries (LIBs). This research proposes a guided sequential immersion cooling (GSIC) BTMS to address this issue. Experimental studies were conducted to evaluate the heat dissipation performance of the GSIC structure under various conditions, including extreme loads. The results indicate that under the static flow immersion cooling (SFIC) scheme, cooling the tabs significantly influences the overall performance. Immersing the tabs can reduce the maximum battery temperature by 10.403 °C, although the spatial variation of temperature persists. Under forced flow immersion cooling (FFIC) conditions, increasing the coolant flow rate dissipates the heat generated by LIBs more effectively. Even at an extreme discharge rate of 5C, the maximum temperature remains below 45 °C. The average temperature reduction at the tabs is greater than the battery body, and with increased flow rates, the temperature difference between the two can be maintained within 1 °C under all conditions. As the flow rate keeps increasing, the average temperature at the tabs gets even lower than the battery body at low loads. This demonstrates that the GSIC BTMS can suppress the temperature rise at the tabs, which is a critical heat risk. Moreover, the temperature uniformity of the LIBs module is improved. As the flow rate increases, the temperature difference within the LIBs module decreases when the discharge rates is between 1C and 5C. Theoretical analysis confirms that increasing flow rates for low loads can suppress temperature rise, albeit with increased power consumption and reduced cooling efficiency. High flow rates are more suitable for high load conditions of the LIBs. These results validate the feasibility of the GSIC BTMS and provide new insights for the development of immersion cooling BTMS.

Effects of multi-element composition regulation on the structure and electrochemistry of P2-type layered cathode materials

P2-type Mn-based oxides are promising cathode materials for sodium-ion batteries due to their low cost and high capacity virtue. However, the irreversible phase transition and unstable anion redox at high operating voltages (∼4.2 V) will cause structural distortions, leading to slow sodium-ion diffusion kinetics and severe capacity degradation. Herein, a multi-elemental composition regulation strategy is proposed to enhance the structural stability of P2-type cathode by optimizing the structure and modulating the irreversible oxygen redox during high-voltage cycling. A series of multi-element cathodes Na0.67(Fe1/4Co1/4Ni1/4Ti1/4)1-xMnxO2 (x = 0.4,0.5,0.6,0.7,0.8,0.9) are designed and the effects of component modulation on their structure and electrochemical behavior are systematically investigated. Especially, the optimized Na0.67Fe0.05Co0.05Ni0.05Ti0.05Mn0.8O2 cathode maintains P2 phase during the initial charging/discharging between 1.5 V and 4.5 V, inhibits irreversible oxygen redox, and exhibits small lattice expansion. Impressively, the above optimized cathode exhibits superior cycling stability with capacity retention of nearly 90 % and reversible capacity of 130.1 mAhg−1 after 100 cycles at 1C rate. Furthermore, the optimized cathode also displays an excellent rate capability (capacity of 108.2 mAh g−1 at 5 C rate) due to the enhanced Na+ diffusion kinetics. This work provides new insight into developing high-stable Mn-based oxide cathodes operating at high voltage for sodium-ion batteries.

Layered Cathode with Ultralow Strain Empowers Rapid-Charging and Slow-Discharging Capability in Sodium Ion Battery.

The development of the electric vehicle industry has spurred demand for secondary batteries capable of rapid-charging and slow-discharging. Among them, sodium-ion batteries (SIBs) with layered oxide as the cathode exhibit competitive advantages due to their comprehensive electrochemical performance. However, to meet the requirements of rapid-charging and slow-discharging scenarios, it is necessary to further enhance the rate performance of the cathode material to achieve symmetrical capacity at different rates. Simultaneously, minimizing lattice strain during asymmetric electrochemical processes is also significant in alleviating strain accumulation. In this study, the ordered distribution of transition metal layers and the diffusion pathway of sodium ions are optimized through targeted K-doping of sodium layers, leading to a reduction of the diffusion barrier and endowment of prominent rate performance. At a 20C rate, the capacity of the cathode can reach 94% of that at a 0.1C rate. Additionally, the rivet effect of the sodium layers resulted in a global volume strain of only 0.03% for the modified cathode during charging at a 10C rate and discharging at a 1C rate. In summary, high-performance SIBs, with promising prospects for rapid-charging and slow-discharging capability, are obtained through the regulation of sodium layers, opening up new avenues for commercial applications.

3D Co-doped carbon nanosheets as high-performance electrodes for Li-S batteries

3D petal-shaped Cobalt-doped carbon nanosheets (PCoCNS) were synthesized as excellent sulfur hosts for lithium-sulfur (Li-S) batteries. Co doping enhanced the affinity of the carbon surface for lithium polysulfides (LiPSs), inhibiting the shuttle effect. The electrocatalytic effect of the PCoCNS electrode exhibited enhanced polysulfide conversion kinetics, thereby promoting Li2S formation. Owing to the above advantages, the PCoCNS cathode exhibited satisfactory reversibility of 841 mAh/g with a high capacity retention of 91 %. Additionally, it displayed high coulombic efficiency (CE) values exceeding 97 % over 100 cycles at a current rate of 0.5C. Furthermore, the electrode demonstrated low polarization and exhibited an excellent rate performance, delivering a capacity of 575 mAh/g at the high rate of 3C. This study synthesized a promising sulfur cathode for enhancing the electrochemical performance of Li-S batteries.

Improving high-voltage cycling and stabilizing the electrode-electrolyte interface of nickel-rich layered cathodes by magnesium doping

Next-generation lithium-ion batteries will rely on nickel-rich layered oxides as cathode materials, but these materials are associated with structural and voltage losses. Magnesium (Mg) doping helps improve the performance of the nickel-rich layered cathode material. The Mg-modified LiNi0·90Mn0·05Co0·05O2 (NMC-90) has been successfully synthesized through a co-precipitation technique followed by calcination at 850 °C. Modified NMC-90 exhibits better-organized layers and improved interfacial properties than pristine ones based on structural, chemical, and morphological studies. In a voltage range of 2.8–4.5 V, Mg (0.01 mol%)-doped NMC-90 (NMC-M1) composite cathode shows an excellent discharge capacity of 211.11 mAh/g, whereas pristine NMC-90 (NMC-M0) attains only 210.59 mAh/g at 0.1C with an initial coulombic efficiency of 89.5 % for NMC-M1 and 87.5 % for NMC-M0 cathode. The NMC-M1 cathode demonstrated an impressive enhancement in cyclability after 60 cycles compared to the NMC-M0 at 1C rate, in which the NMC-M1 cathode attains a high capacity retention of 80 % while the NMC-M0 cathode shows only 37 %. This study illustrates the importance of studying the effects of elemental doping on cell performance. It will drive the future development of cathode materials with high Ni and low Co content.

Low-Solvent-Coordination Solvation Structure for Lithium-Metal Batteries via Electric Dipole-Dipole Interaction.

Unveiling inherent interactions among solvents, Li+ ions, and anions are crucial in dictating solvation-desolvation kinetics at the electrode/electrolyte interface. Developing an electrolyte with a low ion-transport barrier and minimal solvent coordination in its interfacial solvation structure is essential for forming an anion-derived solid-electrolyte interface, a key component for high-performance Li-metal batteries. In this study, we harness electric dipole-dipole synergistic interactions to formulate an electrolyte with significantly reduced interfacial solvent coordination. Operando characterization and theoretical analysis reveal that 2-fluoropyridine (FPy) with high dipole preferentially adsorbs onto the Li metal surface. The adsorbed FPy molecule squeezes succinonitrile in the primary solvation sheath through steric hindrance, leading to the formation of an inorganic-rich interphase. Consequently, the introduction of FPy enhances the reversible capacity of the LiCoO2||Li cell, which maintains a capacity of 143 mAh g-1 after 500 cycles at a 1C rate. Moreover, the cycle life of LiCoO2 batteries with a limited supply of lithium extends from 120 cycles to over 200 cycles. These findings offer a strategy that can be applied broadly to design interfacial solvation structures for various metal-ion/metal-based batteries.

Thermal characterization of pouch cell using infrared thermography and electrochemical modelling for the Design of Effective Battery Thermal Management System

Lithium-ion (Li-ion) cells are the optimal choice of energy storage for battery electric vehicles. As the Li-ion cells must operate in a temperature range of 15–45 °C for optimal performance and life, thermal control of the cells is paramount. The study uses infrared imaging to investigate the temperature dynamics of two lithium-ion pouch cells with two energy capacities, 60 Ah and 20 Ah under different operational scenarios with natural convection. Experimental analysis conducted at ambient temperatures of 27 °C, 35 °C, and 40 °C reveals the necessity of cooling for the 20 Ah cell at temperatures exceeding 40 °C and C-rates beyond 1C. Similarly, thermal management is recommended for the 60 Ah cell at ambient temperatures of 35 °C and above, as temperatures surpass the 45 °C desirable threshold during charging and discharging rates of 1C and higher. Further studies are concentrated on the 60 Ah cell due to its increased cooling demands in comparison to the 20 Ah cell. The 60 Ah cell is modelled using NTGK and ECM electrochemical models and validated against experimental data, showing a good agreement within ±10% between both models and the experimental study. Finally, numerical simulations explain the efficacy of localized cooling with forced convection of liquid and performance metrics are introduced to evaluate the cooling efficiency of design configurations. Based on performance metrics, the T-shaped cold plate design, with an inlet coolant temperature of 30 °C, achieved the highest performance index of 1.13. This design notably decreased the maximum temperature and maximum temperature difference by 41.8% and 31.8%, respectively, compared to natural convection. This improvement is observed during the discharge of 60 Ah cell at 2C in a 40 °C environment, where the cell demands substantial cooling measures. Therefore, implementing localized cooling for the cell demonstrates its effectiveness in regulating temperature increase, leading to a significant decrease in the infrastructure requirements and weight of the thermal management system.

Electrochemical Activation Inducing Rocksalt-to-Spinel Transformation for Prolonged Service Life of LiMn2O4 Cathodes.

LiMn2O4 spinel is emerging as a promising cathode material for lithium-ion batteries, largely due to its open framework that facilitates Li+ diffusion and excellent rate performance. However, the charge-discharge cycling of the LiMn2O4 cathode leads to severe structural degradation and rapid capacity decay. Here, an electrochemical activation strategy is introduced, employing a facile galvano-potentiostatic charging operation, to restore the lost capacity of LiMn2O4 cathode without damaging the battery configuration. With an electrochemical activation strategy, the cycle life of the LiMn2O4 cathode is extended from an initial 1500 to an impressive 14 000 cycles at a 5C rate with Li metal as the anode, while increasing the total discharge energy by ten times. Remarkably, the electrochemical activation enhances the diffusion kinetics of Li+, with the diffusion coefficient experiencing a 37.2% increase. Further investigation reveals that this improvement in capacity and diffusion kinetics results from a transformation of the redox-inert LiMnO2 rocksalt layer on the surface of degraded cathodes back into active spinel. This transformation is confirmed through electron microscopy and corroborated by density functional theory simulations. Moreover, the viability of this electrochemical activation strategy has been demonstrated in pouch cell configurations with Li metal as the anode, underscoring its potential for broader application.

Distribution strategy of flexible phase change materials for pouch battery thermal management considering temperature non-uniformity

Flexible composite phase change materials (CPCMs) have been extensively studied in the thermal management of cylindrical lithium-ion batteries and proven to have a good cooling effect. However, passive cooling of pouch lithium-ion batteries with severe uneven temperature distribution has not received the attention it deserves. The thermal management of pouch battery based on passive cooling of flexible PCMs considering the heat-generating structure of pouch batteries needs to be further studied. Herein, CPCMs with different thermal conductivity were prepared, and four different distribution modes of CPCMs, including partial coverage and complete coverage, were applied to thermal management of pouch battery. Results indicated that the maximum temperature (Tmax) and maximum temperature difference (ΔTmax) can be kept separately within 35 °C and 5 °C in the passive thermal management of a single battery except upper coverage at discharge rate of 5C, and the middle coverage (case B) showed excellent temperature control in partial coverage cases. Equally noteworthy was that the increase in thermal conductivity increased the ΔTmax in partial coverage cases, while showing the opposite trend for full coverage (case ABC). Furthermore, only passive cooling of pouch battery pack did not meet the safety requirements under the discharge rate cycle of 5C. Under the active–passive combination mode, case B can control the Tmax (32.22 °C) and ΔTmax (4.69 °C) within a safe range, which was superior to case ABC (Tmax = 35.53 °C, ΔTmax = 5.04 °C). This conclusion provides technical support for the pouch battery to seek economic, stable and efficient thermal management.

Ultra-high areal capacity, ultra-long life, dendrite-free sodium metal anode enabled by antimony-based Na-ion conducting artificial SEI layers

Sodium metal (Na) is a promising anode material for Na metal batteries and solid-state sodium batteries, because of its high theoretical capacity, favorable electrochemical potential, and cost effectiveness. Nevertheless, practical applications of sodium metal anode are hindered by uncontrolled dendrite growth owing to chemical instability of the heterogeneous solid electrolyte interphase layer. In this work, we proposed a simple interface modification strategy employing several antimony-based Na-ion conducting solid electrolyte complexes as protective artificial SEI layer over Na metal. The Na-ion conducting interphases are robust and highly Na-ion conductive to attain uniform sodium ion flux with a small overpotential. Importantly, Na anode with antimony sulfide based solid electrolyte SEI layers exhibited the high-rate performance (10 mA cm−2) along with a remarkable capacity of 30 mAh cm−2, and life span of ∼ 1100 h. We observe that replacing the conventional artificial SEI layers, employing alloy type interface with Na-ion conducting solid electrolyte as artificial SEI components will improve the mechanical robustness at high current and high-capacity conditions. The sodium metal batteries employing modified metal anodes and high voltage Na1.2Mn0.8O1.5F0.5 cathode, exhibited excellent stability and high efficiency at 1C rate. Furthermore, the modified metal anodes are well-compatible with Na3SbS4 solid-state electrolyte, and the symmetrical solid-state battery exhibited a stable interface. Our strategy holds significant promise and has the potential for widespread application in theadvancement of high-energy sodium metal batteries and solid-state sodium batteries.

Coupling optimization of protruding fin and PCM in hybrid cooling system and cycle strategy matching for lithium-ion battery thermal management

Based on liquid cooling and phase change material (PCM), a fin-enhanced composite thermal management system suitable for high power and extended cycle operations of lithium-ion battery module at high ambient temperature is proposed in this work. The coupling effect between the protruding fin structure and PCM thickness, as well as the addition of expanded graphite to the PCM, are investigated to optimize hybrid cooling arrangement. The results show that synergistic optimization of the protruding fin structure and PCM arrangement can enhance heat diffusion from the batteries to the cooling water, improve PCM utilization, and ensure sufficient latent heat. And then, the expanded graphite-modified PCM can make heat absorption and phase transition more uniform, and battery temperatures can be further decreased by up to 7.45 °C with 16 wt% expanded graphite. Clearly, the coupling optimization improves the cooling performance and applicability of conventional thermal management systems, while the temperature difference and maximum temperature in the optimized system have been regulated to within 4.30 °C and 46.78 °C under 40 °C environment and 5C discharge, respectively. Moreover, the cyclic charging and discharging strategies are designed and matched, and using the matching strategy with a fixed charge or discharge rate of 1C provides lower temperatures and better temperature uniformity, which can always control the temperatures below 47.22 °C and temperature difference below 4.69 °C. The optimized system with cycle strategy matching ensures the repeatability of battery operation and provides cooling solutions for different application scenarios.

Inorganic-organic hybrid heterogeneous membrane for zinc protective layers in high-performance aqueous zinc ion batteries

Aqueous zinc-ion Batteries (AZIBs) suffer from stability and performance limitations due to challenges related to the zinc (Zn) metal anode, including hydrogen evolution reaction (HER), metal corrosion, and Zn dendrite formation. To mitigate these issues, researchers are developing innovative coatings and protective layers for Zn anodes, focusing on enhancing ion conductivity, electrochemical inertness, mechanical strength, and processability. Hybrid organic-inorganic heterostructure coating materials with silver nanowires (Ag NWs) encapsulated with Polypyrrole (Ag/PPy) have shown promise in addressing these challenges. The Zn anode coated with Ag/PPy layers and paired with an α-MnO2 cathode, achieved an impressive initial capacity of 302 mAh/g at a current density of 0.5 A/g. Remarkably, it retained a substantial capacity of 283 mAh/g after 300 cycles at a current density of 0.5 A/g, demonstrating a 94 % capacity retention rate. Moreover, the symmetry cell using this anode maintains stable Zn deposition/stripping overpotentials even at a high current density (a rate of 10C) for over 175 h. These findings highlight the potential of Ag/PPy coatings as a viable approach for enhancing the surface chemistry and physical properties of the Zn metal anode, paving the way for a wider use of AZIBs.

Effect of strontium phosphate coating on NCM811 powders for high-performance Li-ion battery cathode

The NCM811 cathode material, characterized by a high nickel content, is known for its substantial energy capacity but is afflicted by challenges, including electrolyte degradation and inadequate cyclic stability. In this study, a chemical bath deposition technique is utilized to apply a layer of Sr3(PO4)2 material onto the surface of NCM811 particles to address these problems. This procedure yields a continuous protective coating that shields the NCM811 particles from detrimental interactions with the electrolyte, such as HF attack and the formation of surface cracks, while also promoting the diffusion of lithium ions during charge/discharge cycles. XRD analysis indicated that the application of Sr3(PO4)2 coating did not cause any changes in the structure of the NCM811 cathode material. SEM images of all coated samples demonstrated that all coated samples have spherical morphology. Additionally, both Raman and FTIR examinations provide evidences supporting the existence of strontium phosphate material on the surface of the NCM811 cathode material. The distinctive 5.9 nm-thick Sr3(PO4)2 coating enables the NCM811 material to maintain 96 % of its capacity after 100 charge/discharge cycles in a voltage range of 2.8–4.4 V vs. Li/Li+ at a current rate of 1C.

Regulating Li-ion solvation structure and Electrode-Electrolyte interphases via triple-functional electrolyte additive for Lithium-Metal batteries

LiPF6-based carbonate electrolytes have been widely utilized in commercial Li-ion batteries; however, they encounter significant interfacial stability challenges when implemented in high-energy–density lithium-metal batteries (LMBs). Herein, we introduce innovative N,N-diethylcyclohexanamine (NDA) as a triple-functional electrolyte additive to enhance the stability and compatibility of carbonate electrolytes. Due to the high electronegativity of amino group, NDA additive not only eliminates HF/H2O but also modifies the Li+ solvation structure, effectively reducing the electrolyte decomposition, suppressing the hydrolysis of LiPF6 and inhibiting the transition metal (TM) dissolution. Moreover, NDA facilitates the formation of Li3N-rich solid-/cathode-electrolyte interphase (SEI/CEI) layers thought preferential redox reactions at both the lithium metal anode (LMA) and Ni-rich cathode (LiNi0.8Co0.1Mn0.1O2, NCM811), which restrains the growth of Li dendrites, minimizes parasitic reactions, and promotes rapid Li+ transport. Therefore, the Li/NDA-added/Li symmetric cells exhibit remarkably stable cycling performance, lasting up to 630 h at 0.5 mA cm−2/0.5 mAh cm−2. Compared to the baseline cells, the Li/LiNi0.8Co0.1Mn0.1O2 cells with 0.5 wt% NDA show higher capacity retention after 300 cycles at 1C (85.9 % vs. 49.3 %) and superior rate performance, even at 9C. These unique features of NDA present a promising solution for addressing the interfacial deterioration issue of LMBs.

Crystal water-capturing and film-forming bifunctional electrolyte additive for stabilizing sodium iron hexacyanoferrate cathode for Na-ion batteries

Due to its affordability, strong structural stability, and high rate capability, rhombohedral sodium ferrous hexacyanoferrate (FeHCF) has been identified as a potential cathode material for sodium ion batteries. Nevertheless, the presence of inherent crystal water and the susceptibility of its interface stability significantly hinder its capacity and cycling performance. In this study, we propose a novel modification approach involving the addition of ZnCl2 to effectively capture crystal water and facilitate the in-situ formation of a ZnO coating on the FeHCF surface. Due to the decreased crystal water content and the presence of stable ZnO interphases, the occurrence of side reactions between the electrode and electrolyte, as well as crystal particle cracks in FeHCF during repeated sodiation/desodiation processes, is effectively reduced. Consequently, the modified FeHCF demonstrates an extended operational lifespan of 1000 cycles, with an initial discharge capacity of 112.0 mAh/g and a capacity retention rate of 77.8 % at a current rate of 1C within the voltage range of 2.0–4.2 V. Our research offers valuable insights into the removal of crystal water and the engineering of incident interfaces to enhance the cycle life of FeHCF cathodes in sodium-ion batteries.

High-Viscosity Phase Inversion Separators for Freestanding and Direct-on-Electrode Manufacturing in Lithium-Ion Batteries.

Separators play a critical role in lithium-ion batteries (LIBs) by facilitating lithium-ion (Li-ion) transport while enabling safe battery operation. However, commercial separators made from polypropylene (PP) or polyethylene (PE) impose a discrete processing step in current LIB manufacturing as they cannot be manufactured with the same slot-die coating process used to fabricate the electrodes. Moreover, commercial separators cannot accommodate newer manufacturing processes used to produce leading-edge microbatteries and flexible batteries with customized form factors. As a path toward rethinking LIB fabrication, we have developed a high-viscosity polymer composite separator slurry that enables the fabrication of both freestanding and direct-on-electrode films. A streamlined phase inversion process is used to impart porosity in cast separator films upon drying. To understand the impacts of material composition and rheology on phase inversion processing and separator performance, we investigated four different separator formulations. We used either diethylene glycol (DEG) or triethyl phosphate (TEP) as a nonsolvent, and either silica (SiO2) or alumina (Al2O3) as an inorganic additive in a polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) matrix. Through a down-selection process, we developed a TEP-SiO2 separator formulation that matched or outperformed a commercial Celgard 2325 (PP/PE/PP) separator and a Beyond Battery ceramic-coated PE (CC/PE/CC) separator under rate and cycle life tests in LiFePO4|Li4Ti5O12 (LFP|LTO) and LiNi0.5Mn0.3Co0.2O2|graphite (NMC-532|graphite) coin cells at C/10-1C rates. Our TEP-SiO2 slurry had a viscosity of 298 Pa s at a 1 s-1 shear rate and shear-thinning behavior. When deposited directly onto an LTO anode and cycled against an LFP cathode, the direct-on-electrode TEP-SiO2 separator increased the specific capacity by 58% and 304% at 2C rates relative to the PP/PE/PP and CC/PE/CC separators, respectively. Additionally, the freestanding TEP-SiO2 separator maintained dimensional stability when heated to 200 °C for 1 h and demonstrated a higher elastic modulus and hardness than the PP/PE/PP and CC/PE/CC separators when measured with nanoindentation.